Necessary Assumption vs Sufficient Assumption - How to Gage Strong Language?

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• 3 Likes

  foxtrot96 Member

  August 2018 147 karma

  think of it this way, for Sufficient assumption questions, you are looking for an answer that absolutely guarantees that you get from Premise A to conclusion B. this is why the strongly worded answers are generally indicators of a sufficient assumption answer instead of a necessary one.

  On necessary assumption questions however you are looking for something that doesnt have to absolutely guarantee A---> B assumption but instead is an assumption that absolutely has to be true for the argument to work and generally the authors try to do that in subtle ways which is why most necessary assumption answers are weakly worded in contrast to the sufficient assumption answers that are strongly worded.

  this is not to say that strongly worded answers can never be necessary assumptions but be wary of strongly worded answers and be sure if its works as a sufficient asusmption or as a necessary assumption. for more difficult questions a strongly worded answer choice could be a necessary assumption too.

  What would help you though is to understand that we are looking for an answer that absolutely has to be true for the argument to work so work with the mindset of finding a MBT answer instead of getting bogged down by weakly worded or strongly worded distinction. Treat them like a MBT question and you'll see that it becomes easier to spot the correct answer this way.

  "What absolutely has to be true to make the argument work?"
• GreatDay8 Alum Member

  August 2018 130 karma

  @foxtrot96 Thanks for the reminder that the weakly vs. strongly worded distinction shouldn't bog me down, nor should it be used as my main method of identifying the correct AC. So far I have been negating the answer choices to see which one absolutely wrecks the argument, which has been working. I haven't really used the MBT method of approach so I'll give it a try. Thanks for the response!
• 2 Likes

  Ohnoeshalpme Alum Member ⭐

  August 2018 2531 karma

  As stated above, it is more of a guideline than a rule. I always think back to the basketball example: "Jerry is the best basketball player that ever lived" a necessary assumption here is "Jerry could hold a basketball" or "Jerry could walk". They speak only to what is at very least necessary for this statement to be true. The LSAT writers put these question types in because it weeds out a lot of test takers who mistake them for sufficient assumptions or strengthening questions. Once you get better with NA questions, the answers will just pop out to you. And the method of negating correct answer choices is a good way to make sure you're not falling for a trap answer choice.
• 1 Like

  jhbm_nyc Alum Member

  August 2018 edited August 2018 568 karma

  Agreed with the above posts. NA is often weak compared to SA, but it's certainly not a hard and fast rule. An argument with a strong conclusion will call for a strong necessary assumption. In some arguments, especially simple ones, the correct answer choice can be both a NA and SA.

  Here's a common example used to illustrate the difference. Say you walk into a store to buy a jacket and find out it costs $100. You conclude, therefore, you can afford the jacket. A SA would be "You have a million dollars"--this is great because it definitely guarantees the conclusion. But it doesn't have to be true. If you negate it to say you only have a thousand dollars, our argument still stands. On the other hand, a NA would be "You have at least $100"--this has to be true for the argument to work. If you negate it to say you have less than $100, you wreck the argument.

  Here's a more complex example, which is an analogy of a real NA question I just reviewed. "Doctors who publicly endorse herbal medicine, while effective for some patients, will most likely taint their credibility. Therefore, doctors should never publicly endorse herbal medicine."

  SA: "Doctors should never publicly endorse a product if there is any chance that they will taint their credibility." Any chance is too strong. This says that even a 1% chance is enough of a reason to not publicly endorse. But our premise just says "most likely," so more than a 50% chance. Negating "any chance" to say "tiny chance" (say 3%) doesn't touch our argument, which is only concerned about >50% chance.

  NA: "Doctors should never publicly endorse a product if there is a high chance of tainting their credibility as a result." High chance matches our premise. This has to be true. Negating it -- it's ok to endorse even if there's a high chance -- wrecks our argument.
• 1 Like

  AshleighK Alum Member

  August 2018 786 karma

  Also keep in mind the different types of NA - Is it a shielding or a bridging type? This helps me with hunting for the correct AC.

  Shield: protects the idea
  Bridging: basically like SA

  And ofc use the negation trick. If you get stuck the easiest thing I could say is just drill a couple of NAs back to back and work on memorizing your negations so this can be done quickly. There's always a few NAs in LR so it's good to try to bank on them - if it's a big weakness skip it and come back to it
• GreatDay8 Alum Member

  August 2018 130 karma

  Thanks guys. @jhbm_nyc Negating likelihoods in your herbal medicine example - aside from it being a great mental exercise - helped me to see that the "any chance" was too strong for what was necessary. Thanks